1. Field of the Invention
The present invention relates to an X-ray CT (computed tomography) apparatus including an X-ray CT gantry in which strength and rigidity are improved.
2. Description of the Related Art
X-ray CT apparatuses have become widespread as apparatuses for medical diagnosis (see, for example, Japanese Patent Application (Laid-Open) No. 2000-116644). X-ray CT apparatuses include a gantry incorporating an X-ray tube, a detector, a power supply, and components for processing a signal. An imaging opening for imaging an object is formed in the central portion of the gantry of the X-ray CT apparatus. Components including the X-ray tube and the detector are contained in a box-like container member, which is a part of the gantry, and are arranged on either side of the imaging opening.
In a helical scan X-ray CT apparatus, components including an X-ray tube and a detector rotate about an object to be imaged, and therefore, the components including the X-ray tube and the detector form a rotating unit. The whole body of the X-ray CT apparatus is surrounded by a cover to protect the inside of the X-ray CT apparatus.
FIG. 14 is a front view showing a structure of a conventional X-ray CT apparatus. FIG. 15 is a side view of the conventional X-ray CT apparatus shown in FIG. 14.
An X-ray CT apparatus 1 includes a gantry 2. The gantry 2 is surrounded by a cover (not shown). The gantry 2 includes a rotating part 3, a mainframe 4, and a stand 5. The rotating part 3 includes a donut-shaped rotating base 3a, which incorporates an X-ray tube, a high-voltage generation unit, a detector, a board for controlling X-rays and other components, and electric components, e.g., power supply (each not shown). The interior of the rotating part 3 serves as an imaging area S. Additionally, the rotating base 3a of the rotating part 3 is mounted on the planar mainframe 4 with a bearing 6 therebetween. A shaft-like supporting unit 7 is provided on either side of the mainframe 4. The axis direction of the supporting unit 7 is horizontal and substantially perpendicular to a rotation axis of the rotating part 3.
On the other hand, the stand 5 includes supporters 8 each perpendicular to the mounting surface of the X-ray CT apparatus 1, an extendable rod-like actuator 9, and electric components 10 contained in a metallic box. The supporting unit 7 mounted on either side of the mainframe 4 is supported by the supporter 8 of the stand 5 in a rotatable manner about the axis of the supporting unit 7. Furthermore, the other part of the mainframe 4 is supported by the actuator 9.
Accordingly, the rotating part 3 and the mainframe 4 are tiltable about the axis of the supporting unit 7 so that a two-dimensional image data of an object can be obtained at a desired angle.
Additionally, an X-ray CT apparatus has been proposed in which a LM (Linear Motion) guide is provided on either side of a stand to maintain the supporting rigidity of a gantry (see, for example, Japanese Patent Application (Laid-Open) No. H6-178769).
However, in a known X-ray CT apparatus having a tiltable gantry, a backlash occurs between a tilt structure and a supporting unit and between a stand and the supporting unit. Therefore, when obtaining a high-resolution image in an area in all the radial directions of a rotating part, the error corresponding to the backlash has an adverse effect on the image, which is a problem. It is known that, as the inner diameter of the rotating part (i.e., the imaging area) increases, the effect of the backlash on the image becomes more significant. In addition, recently, the imaging area in a radial direction of an X-ray CT apparatus has become larger. As a result, to reduce the error caused by the backlash, a damper is provided at a variety of locations of the X-ray CT apparatus. Also, a special positioning process is performed. That is, extra components or extra man-hours are required to reduce the error.
Furthermore, in recent X-ray CT apparatuses, a gantry including a rotating part rotating at high speeds is generally used. Accordingly, even a slight imbalance may cause a large force, and therefore, adjustment of the balance is critical. However, it is difficult to completely eliminate the imbalance, and therefore, a stand serving as a base is required to be reinforced as well as the whole gantry.
Still furthermore, in recent X-ray CT apparatuses, a two-dimensional detector having detecting elements of which each size is about 0.5 mm by 0.5 mm is generally used. Accordingly, various factors including a backlash in a tilt structure cause vibration of the gantry. The vibration of the gantry has a serious impact on the image quality.
In a known X-ray CT apparatus including an LM guide, the strength of a gantry depends on the strength of a stand. Accordingly, even when the rigidity of the LM guide which is provided on either side of the stand is increased, the increase in the rigidity does not directly result in the increase in the rigidity and strength of the gantry. Also, since two costly LM guides are necessary, this solution is not desirable in terms of cost effectiveness.